The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

No rehab for Vic blackmail niece: court

An apparent lack of resources has placed a Melbourne judge into the "lamentable" situation of being unable to immediately sentence a former airline cleaner, who wants to be jailed for blackmailing her uncle.

Lydia Jasmine Vonja, of Maidstone, has pleaded guilty to repeatedly calling her paranoid schizophrenic uncle pretending to be a detective and demanding he pay outstanding parking fines.

The 37-year-old began offending to fund a $200-a-day heroin and ice addiction, the Victorian County Court heard.

She does not want to be released on a community corrections order (CCO) because she fears she will relapse.

Vonja told her uncle to put amounts ranging from $200 to $4000 in his letter box between December 2 and December 13 last year and threatened to take away his licence and his car if he did not pay-up, Prosecutor Patrick O'Halloran said.

Vonja's uncle handed-over $12,500 before he learnt he was being tricked and refused to pay, at which point Vonja said: "You put the money in the letterbox or I will kill you", the court heard on Thursday.

Defence barrister Rebekah Sleeth said Vonja wanted to be sentenced to a period in prison, because she did not feel ready for release.